Blender smoke sim explosion just ends up like volumetric fog
You need to tell the Principled Volume node where to get it's measure of the 'density' of the domain from. You can do this by either feeding a value into the 'Density' socket or you can fill in the 'Density Attribute' to indicate it should be taken from the smoke domain 'density' attribute.
In your case you should be able to simply click on the 'Density Attribute' field and enter 'density' (all lower case).

Changing the 'Density' value (just above the Density Attribute) will adjust overall density of the smoke (it acts as a multiplier).